1. Field of the Invention
The present invention relates to a print head that can form an image by ion projection or light emission caused by an electric discharge, and relates to an image forming apparatus including the print head.
2. Description of the Related Art
In recent years, an ion projection method that is an electrostatic latent image forming method different from an electrophotographic method has been developed (see Japanese Published Unexamined Patent Application No. 2003-326756, mentioned below, for example).
According to the electrophotographic method, an electrostatic latent image is formed on a photoconductor serving as an electrostatic latent image carrier by expelling an electric charge of an exposed part on the uniformly electrified photoconductor through two steps consisting of a uniform charging step and an exposure step. On the other hand, according to the ion projection method, in an atmosphere (for example, in atmospheric air) in which ions can be generated, the formation of an electrostatic latent image on an electrostatic latent image carrier (which is not necessarily required to be a photoconductor, because what is required of the carrier is to be an insulator) can be completed by selective electrification (electrostatic-latent-image forming electrification) by ion projection caused by an electric discharge from a discharge electrode. Therefore, the ion projection method is an electrostatic latent image forming method that has been made simpler and that does not need to use an exposure optical system such as a polygon mirror.
An image forming apparatus employing the electrostatic latent image forming method using the ion projection method can directly form an electrostatic latent image by ion projection on a recording medium of an electrostatic development type which is typified by digital paper and in which a visible image appears while reacting to the electric charge of an electrostatic latent image formed on its surface. Therefore, under the circumstances, this apparatus is the best conceivable image forming apparatus, in order to write data onto the electrostatic development type recording medium in a noncontact manner (see FIG. 4 of Japanese Published Unexamined Patent Application No. JP 2003-326756).
At present, digital paper can be achieved according to the following methods, i.e., a twist ball method in which extremely small balls are classified into two colors (for example, black and white), and an arbitrary color is displayed by rotating the balls according to a difference in electric characteristics of each color; an electrophoretic method in which impalpable powder with two colors (for example, black and white) is mixed with extremely small balls, and only one color is surfaced and displayed by a difference in electric characteristics of impalpable powder of each color; and a liquid crystal method in which a liquid crystal shutter of a liquid crystal plate or an extremely small liquid crystal block is opened or closed, and a background color of a part appearing by opening the shutter is displayed.
However, Japanese Published Unexamined Patent Application No. 2003-326756 merely discloses a basic concept of a digital-paper-acceptable apparatus that includes an ion generating device or a regular-paper-acceptable apparatus that employs an electrostatic latent image forming method having no optical system. In other words, Japanese Published Unexamined Patent Application No. 2003-326756 disclosing the image forming apparatus gives no description of, for example, a detailed structure of a print head. Especially, a study has been expected to be made of the concrete specifications of a print head suitable to record data on a thick recording medium such as digital paper.
A rewritable recording medium, such as digital paper, is assumed to be repeatedly used about several thousand times. To satisfy this severe durability, a conventional problem resides in the fact that there is a need to develop a horizontal-printer-usable print head that can perform a writing operation in a state in which the recording medium is not bent in order for the recording medium not to cause a distortion as much as possible when used.
Another conventional problem resides in the fact that there is a need to develop a print head corresponding to shapes of various electrostatic latent image carriers (ion projected body), such as a drum type carrier or a belt type carrier, when an electrostatic latent image is written onto the electrostatic latent image carrier in a regular-paper-acceptable apparatus that employs an electrostatic latent image forming method.